THE MALADETA GRANITE POLYDIAPIR, SPANISH PYRENEES - A DETAILED MAGNETOSTRUCTURAL STUDY

The Maladeta granitic complex (Spanish Central Pyrenees) has been subjected to a detailed magnetostructural study, through the systematic measurement of magnetic susceptibility and anisotropy of magnetic susceptibility at 253 regularly spaced sampling sites. Due to the dominant paramagnetic property of the granites, a first-order correlation can be derived between the susceptibility magnitude and the bulk-rock iron content, hence the petrographic nature of the rock. The Maladeta complex is shown to be composed of four principal juxtaposed plutons, each one being normally zoned, i.e. becoming more basic towards the periphery. The largest pluton, namely the Colomers unit, is itself made of a number of sub-plutons due to distinct but more-or-less coeval batches of magmas. The various magnetic data, complemented by field and microstructural observations, allow us to propose that the Maladeta polydiapir probably exploited NE- and SE-trending openings of the brittle crust for its emplacement, that accompanied or just preceded a SW-verging compressive event. A later N-S compression marked by inverse dextral, and E-W-trending shears, is preferably attributed to late Variscan rather than to Alpine tectonics.